Ignition system



Aug. 17, 1937. P. o. STEWART- IGNITION SYSTEM Filed Maren 21, 1934 2 sheets-sheet 1 INVENTOR BY m ATTORNEYS Aug. 17, 1937. P. o. STEWART IGNITION SYSTEM Filed March 21; '1954 2 Sheets-Sheet 2 WWW (a? lNVENTOR ATTORNEYS Patented Aug. 17, 1937 f UNITE gestalt PATENT QFHE 2 Claims.

My invention relates to a new and improved system for suppressing undesirable electrical osoillations which are produced by the ignition system of an automobile, so that said oscillations will not injuriously affect the reception of a radio receiving set which is connected to the storage battery of the automobile.

One of the objects of my invention is to provide a universal suppressor or choke, which can be readily applied to all of. the standard spark plugs which are now in use in American automobiles.

Another object of my invention is toprovide the improved suppressor with certain auxiliary parts which will make it universally applicable to all standard makes of American automobiles.

Another object of my invention is to provide an improved system for properly designing and locating the inductances and capacities of the ignition system, so that the undesirable oscillations will be suppressed, while delivering sub-- stantially full ignition current to the spark plugs.

Another object of my invention is to provide a system for suppressing undesirable oscillations, without affecting the efficiency of the ignition system.

| Another object of my invention is to provide simple, compact and eflicient means for varying the inductances of the various choke coils which are used as suppressors.

Other objects of my invention will be set forth in the following description and drawings which illustrate a preferred embodiment thereof, it being understood that the above statement of.

the objects of my invention is intended to generally explain the same Without limiting it in any manner.

Fig. l is an elevation showing the improved suppressor applied to a spark plug.

Fig. 2 is a vertical sectional view through the suppressor.

Fig. 3 is a sectional view along the line 3-3 of Fig. 2.

Fig. 4 is a top plan view of the suppressor.

Fig. 5 is a sectional View on the line 5-5 of Fig. 1.

Fig. 6 is an elevation showing the application of the auxiliary parts to the suppressor.

Figs. 6a and 6b illustrate certain details.

Fig. 7 is a general diagrammatic view illustrating part of the ignition system of an automobile and the application of the suppressors.

Fig. 8 is a diagrammatic view of the electrical circuit involved.

As shown in Figs. 1 and 2, the suppressor comprises an outer shell or casing l. which is made of bakelite or other suitable insulating material which can be readily molded or worked. The top of the casing i is integral therewith and the bottom of said casing is provided with a cover 2 5 which is also made of any suitable insulating material. This insulating material may be a phenol-formaldehyde condensation resin.

The top of the casing l is integral with a central core 3, which is also made of said insulating 10 material and said core extends substantially to the cover 2. The choke coil C is wound between the inner wall of thecasing I and the core 3.

The choke coil is separated from the top and bottom of the casing, by insulation 4, which 15 is made of suitably treated paper or the like. The choke coil C is made of any suitable Wire, such as copper wire of .004 gauge. This wire is provided with a thin covering of enamel.

The choke coil C is of standard construction.

In the practical manufacture of the choke coil, the wire is first/wound upon a paper tube P. A single helical coil of wire is Wound upon the paper core or tube P, and a piece of insulating paper is then formed into cylindrical shape and 25 it is applied over said first helical layer of wire, and said initial intermediate paper sheet is then suitably secured into position, by a suitable adhesive. The wire is then formed into a second helix over said first paper sheet. 30

A second sheet of paper is then applied over the second helix, and this process is continued until the choke coil has been built up to the proper number of layers of turns, each pair of layers having an intermediate sheet of. insulating pa- 35 per.

The end insulation 4 comprises a series of paper layers which are extensions of the intermediate layers which are used in forming the choke coil C. When this coil has been completed, it is 40 slipped over the core 3. The core 3 is internally threaded, in order to receive an externally threaded stud 5, which projects from the top of the easing. A nut '6 is mounted upon the externally threaded stud 5 and this nut 6 clamps a stamped 45 metal lug 1, against the top of the casing. The lug l is provided with an extension la which fits into a depression which is formed between upstanding lugs la of the casing l. Said projections I a. are also made of said insulating mate- 5O rial and the extension la. fits snugly in said depression.

The choke coil C is provided with a top lead 8 which passes through a hole in the top of the casing, and said lead is bent horizontally so as to 55 overlie the extension 1a and the horizontal branch of said lead 8 is soldered to the top of the lug Ia. This soldering, together with the fit of the extension la in the recess between the pro- 5 jections la, prevents the lug I from turning when the nut B is applied. The nut 6 can also be connected by solder to the lug 1 so that the members 9 and I are held against turning on the stud 5, after the assembly has been completed.

10 The cover 2 is held in position by means of a dual threaded connector 9, which is provided with external ribs 59, in order to dissipate the heat which is conductively transmitted to the connector 9, from the spark plug. The connector 9 is provided with an externally threaded projection lila, which enters an internally threaded recess in the core 3. The choke coil is provided with a lower lead 811, which passes through a. hole in the cover 2 and said lead 8a passes over and is soldered to the extension |2a of the metal lug l2.

The extension |2a fits between projections 2a of the cover, and said projections 20. correspond to the projections Ia which have been previously described.

The lug 2 is clamped into position against the cover 2 by the turning of the projection la in the internally threaded recess of the core 3. Likewise the lug I2 is connected to the adjacent flange |5b of the connector 9 by means of solder, 39 and since the wire or lead 8a is also connected to the bottom of the extension |2a by means of solder, the parts are held together without any danger of relative movement, after the assembly has been completed.

The interior of the connector 9 is provided with a thread M and with a second thread Ma. The pitch of thread l4 corresponds to what is known in the trade as 10/32. That is, the pitch of said thread is (one thirty-second) of an inch 40 and it is adapted to receive a No. 10 screw or stud. The thread Ma corresponds to what is known in the trade as 8/32. That is, the pitch of thread Ma is (one thirty-second) of an inch and it can receive a No. 8 screw or stud.

Referring to 1, this shows a spark plug S having the usual terminal which is externally threaded. In standard American practice said terminals are either 10/32 or 8/32. A 10/32 terminal can be received in thread I and an 8/32 terminal can be received in thread Ila, so that the suppressor can be universally applied.

Fig. 3 shows means for regulating the inductance of the coil. As shown in Fig. 3, the interior wall of the casing I may be provided with recesses l5, and the core 3 may be provided with recesses |6. Magnetic cores l1 and Na, in any desired number, may be inserted into :saidrecesses I5 and l5. These magnetic core members are made of soft iron and they serve to vary the inductance of the choke coil.

The core members I1 and l'la are preferably made of minute iron particles which are connected by means of particles of bakelite or other suitable material, inorder to form molded masses of cylindrical shape. These core members provide higher magnetic leakage for the high frequency component of the ignition current, so that the inductance of each suppressor can be varied as desired. 7

A thimble l8, having an internally threaded recess in its bottom wall, can be threaded upon the stud 5. This thimble |8 provides a connector of the socket type for receiving the wire from or to the ignition coil, when the device is used for E5 connecting the ignition coil to the distributor.

The thimble l8 provides a socket connection forv any desired location in which the device may be used.

Instead of using a connector of the socket type 58, an internally threaded thimble l9 may be screwed over the stud 5, as shown in Fig. 6.

The thimble I9 is provided with a. flange |9a and a forked terminal of the Rajah type may be placed under the flange |9a in order to connect with the stud 5. Other types of connectors may be slipped over the thimble I9 to rest upon the flange l9a.

In order to install the suppressor upon either the distributor or the ignition coil, a threaded stud 20 can be inserted into the thread Ma. A split bushing 2| can be threaded on the bottom portion of the stud 20. The split bushing 2| is provided with a head 2|a.

The stud 29 is of substantially cylindrical shape, and it is provided with an outer thread of uniform width to its bottom. The stud 20 can first be screwed into the threaded part Ma. The split bushing 2| can then be located upon said stud 29. The split bushing 2| is then inserted into the socket of the distributor or of the ignition coil and the suppressor can then be turned in the clockwise direction.

The internal thread of the split bushing 2| is inwardly tapered. When the suppressor I is turned, the stud 28 is pushed into the inwardly tapered thread of the bushing 2|, so that the bushing H is expanded in order to fit tightly into the corresponding socket.

Instead of using the split bushing 2 l, I can use the internally and externally threaded bushing 23, for making contact with coils or the like which have threaded openings in their shells for making connection.

Referring to Fig. '7, this shows four of the spark plugs of an internal combustion engine which,

may have any desired number of cylinders and spark plugs. Fig. 7 shows a suppressor provided for each of the spark plugs and it also shows a suppressor provided for the distributor D, which is of any suitable type. nition coil or step-up transformer Ca, whose primary'coil 3c is connected to the battery Ba in the usual manner.

A suppressor is also provided directly adjacent the ignition coil.

In the conventional type of ignition system which utilizes a distributor, the primary coil is connected to the terminals of the storage battery, and a secondary coil is utilized for stepping up the voltage to several thousand volts, when the primary circuit is opened.

Each of the units of the ignition system has a certain capacity. For example the coils of the ignition coil Co have a capacity, the lead A from the coil to the distributor has a capacity, and each of the leads B from the distributor to the individual spark plugs has its own capacity.

When the ignition current discharges through a spark plug, said ignition current has a certain unidirectional current pulse, which should not be diminished or interfered with in any manner, and said ignition current has a high frequency alternating current component, which produces a number of rapidly damped oscillations, and said oscillations must be suppressed without diminishing the unidirectional current pulse. This unidirectional current pulse increases to a certain maximum and it then diminishes to zero.

While previous suppressor systems have been efficient in suppressing the undesirable high ire- Fig. '7 also shows the igquency component; they have materially diminished the directcurrent pulse, so as to interfere with the proper performance of the engine. In previously known and commercially used systems, each spark plug was provided with a high resistance which prevented or rapidly damped the high frequencycurrent, but these resistances diminished the ignition current.

Referring to Fig. 8, this shows the storage battery Ba, the primary coil 30, the secondary coil 3i of the ignition coil Ca, and this also shows a single spark gap Sa.

- Fig. 8 also shows a switch 32, for opening and closing the circuit of the primary coil 30, this being the breaker switch of the distributor D. When the switch 32 is opened, the stored electrical energy which is represented by the inductance and capacity of the secondary circuit, discharges through the selected spark gap.

As shown in Fig. 8, the secondary coil 3| has a natural capacity which is represented by an imaginary condenser E, the lead A has a natural capacity which is represented by imaginary condenser E, and the lead B from the distributor D to the spark plug, has a natural capacity which is represented by imaginary condenser E I provide a choke coil or inductive suppressor C in association with each of these natural capacities.

The secondary circuit is therefore divided into a series of sections, each of which has its own natural capacity and its own inductance or choke coil. The choke coils may have their inductances properly selected, in order to correspond to the natural capacities of the line components.

For example, the leads B which go to the various spark plugs, may be of diiferent lengths and different inductances will therefore be provided to match the corresponding differences of natural capacities.

However, in actual practice, choke coils of equal inductance may be used.

When the primary circuit is opened, the voltage at the terminals of secondary coil 3| rises rapidly from zero to several thousand volts, until the voltage is high enough to break down the re sistance of spark gap So. It will be noted that the secondary and primary coils have their adjacent ends grounded. In the old system, in which a single high resistance was placed upon each spark plug, the natural capacities represented by E, E and E were charged until the break-down voltage was built up. When the spark passed across the gap So, its resistance was materially lowered. The capacities of the ignition circuit elements were arranged in parallel, and said capacities discharged through the high resistance which was located at the top of the spark plug.

Sometimes a high resistance leak was installed at the distributor. This high resistance of the secondary circuit, during the passage of the spark, prevented or rapidly damped high frequency oscillations.

The decay of the high self-inductance of the secondary coil produced a unidirectional current pulse which rose from zero to a certain value, and then dropped to zero. This current pulse produced the ignition, but it was materially lowered by the high resistance, especially at high engine speed.

According to the improved system or circuit, the secondary circuit of the ignition coil is divided into three separate sub-circuits, each of which can freely oscillate when the discharge takesplace. The first sub-circuit comprises capacities E and E and the intermediate choke coil. The second sub-circuit comprises capacities E and E and the intermediate choke coil. The third sub-circuit comprises capacity E and the choke coil on the spark gap. These three circuits have capacity couplings which are pro duced by capacities E and E Each of these three circuits may have the same frequency of free oscillation, by suitably regulating the inductances, and this is preferred, as this type of oscillation minimizes transfer of energy between the oscillating sub-circuits. However, such equal periods are not necessary.

In the improved circuit, when the discharge takes place, the three sub-circuits oscillate. The frequency of said oscillations is high because each sub-circuit has a capacity which is less than the total capacity of the ignition circuit. Due to the high frequency and since the oscillations are rapidly clamped in each sub-circuit, the undesirable electrical oscilations are suppressed and without substantially diminishing the unidirectional current pulse which maintains the spark.

The improved circuit also makes it possible to use a plurality of choke coils whose total inductance is low. This low inductance diminishes the reactance of the circuit relative to the unidirectional current pulse.

While I prefer to use three sub-circuits as being the best embodiment of my invention, I wish to include a system which has only two subcircuits (by eliminating one of the choke coils shown in Fig. 8), and I may use more than three sub-circuits.

The ignition coil may be replaced by a magneto or other source of current of high potential.

In effect, the first inductance is located substantially between the secondary coil and conductor A, the second inductance is located substantially between the distributor and conductor A and the third inductance is located substantially between the spark plug and conductor B. That is, the capacity of the connection between the first inductance and the secondary coil, or the capacity of the connection between the second inductance and distributor D, is less than the capacity of conductor A.

Likewise, the capacity of the connection between the third inductance and the spark plug is less than the capacity of conductor B. The capacities of the circuit are therefore substantially represented by the imaginary condensers which are shown in Fig. 8.

As a practical example of my invention, eight choke coils were installed in a six-cylinder 1933 De Soto automobile. Each of these choke coils had a resistance of 110 ohms, and an inductance of 0.017 henry at a frequency of one thousand (1000) cycles per second. However, said coils are effective as choke coils, at frequencies which are as high as one million cycles per second. One coil was on top of each spark plug, one was on the distributor and one was on the ignition coil. Tests on a dynamometer, while the car was running, showed no lowering of power at road speeds from 10 miles per hour to 60 miles per hour. In the old system, which used high resistances, there is a loss of from 5% to 12% in this range of speeds. Tests were made with a direct current milliammeter in the ignition circuit, with and without the choke coils and such tests showed no perceptible decrease in the direct current component of the ignition current.

This was due to the fact that the total resistance which was added to each spark gap, Was only a very small fraction of the resistance of the gap circuit, prior to the passage of the spark. Tests showed that the standard high-resistance leaks diminished the ignition current from 20% to 50%. When the standard high resistance leaks were used, the maximum high speed of the car was lowered. When the choke coil at the ignition coil was removed, a slight clicking sound would be heardin the radio reception. When the three inductances in each spark gap circuit were coupled in series directly to the spark plug, a pronounced clicking was heard, and this arrangement was of no practical value.

Ihe division of the ignition circuit into oscillatory sub-circuits may be accomplished by lowering the capacity of the elements of the circuit, instead of increasing the inductance. For example, the capacity'of the conductors A and B voltage current whose circuit includes a distributor which is connected to said source by a first conductor and a spark plug which is connected to said distributor by a second conductor, a first inductance which is located substantially between said source and said first conductor, a second inductance which is located substantially between said distributor and said first conductor, and a third inductance located substantially between said spark plug and the second conductor, said inductances being sufficiently high to divide said circuit into three sub-circuits which can freely oscillate, each sub-circuit including one of said inductances.

2. In an ignition system for an internal combustion engine which comprises a source of high voltage current whose circuit includes a distributor which is connected to said source by a first conductor .and a spark plug which is connected to said distributor by a second conductor, a first inductance which is located substantially between said source and said first conductor, a second inductance which is located substantially between said distributor and said first conductor, and a third inductance located substantially between said spark plug and the second conductor, said inductances being sufficiently high to divide said circuit into three sub-circuits which can freely oscillate, the natural frequencies of said sub-circuits being substantially equal.

PATTERSON O. STEWART. 

